Inductive heat treating apparatus



May 20, 1941. H. E; soMEs INDUQTIVE HEAT TREATING APPARATUS Filed Oct. 25, 1938 `mumlllllllllllllllllllllllllllllllllllllnm mum H Howard E. Homes: BY aff (P. (@J# ATTORNEY breakdown or the like.

Patented May zo, 1941 UNITED STATES PATENT oFFlcE INDUCTIVE HEAT TREATING APPARATUS Howard E. Somes, Grosse Pointe Park, Mich.

Application October 25, 1938, Serial No. 236,872

(Cl. 21S-d3) 2Claims.

apparatus. In that application there is disclosed an apparatus in which an induction heating element in the form of a coil having a magnetic core element is arranged to be inserted in a hollcw work-piece of magnetic material, for example, within the inner cylindrical portion of an iron wheel hub, engine cylinder or the like, the work-piece acting to complete, or form a substantial part of a magnetic circuit conducting element of high permeabilityl for the heating coil. A pair of relatively short circuit conductor elements connect the heating coil to a source of high frequency current for energizatlon thereby, the circuit formed by the coil and the said conductorsl being tuned or adjusted by connection therewith oi a suitable condenser or cnndensers for power-factor correction of the circuit under the electrical conditions which exist when the heating coil is in operative relation with the work-piece, In the normal operation of such a machine upcn work-pieces substantially identical 'and to which the machine is adjusted to maxi' mum eiiiciency, the operationsare found to be uniform with substantially .no undesirable electrical effects such as undue arcing, insulation due to some accidental lvariation in the character of the work-piece, severe electrical disturbances are produced which manifest themselves in resistance breakdown or arci'rig over between insu' lated portions of the circuit, particularly near the terminals of the inductive heating element and at points aong the conducting elements connecting the heating coil or work circuit with the source of current supply.

In practice, it is noted that such pJints of disruptive discharge occur at diiierent places at different times.

While the causes of such phenomena are not definitely understood at present, at least not sufilciently to attempt to explain them at this time,

it has been observed. that the phenomena usually occur when an attempt is made to operate upon the defective work-piece, for example one that varies widely in iiullty of material, internal However, occasionally, v

struct-ure or even shape and size, from that of the standard type of work-pieces to which the machine is adjusted, or pieces that have a tendency to crack during treatmentresulting in a flashing over at the cracked portion, and it is believed that such imperfections in the workpiece bring about sudden electrical changes in the circuit of the apparatus, for example a sudden reduction or other variation in the permeability of the magnetic circuit of the heating coil or other sudden electrical changes thus'producing transient currents in the circuit o! the apparatus, perhaps of extremely high frequency, resulting in the establishment of an excessively high. potential at certain points with nodes of substantially zerc potential at other points such as would be produced by a high rrequency stationary voltage wave in the circuit of the apparatus, the location cf such crests and nodes varying according to the length of such stationary wave. This would account for the variation in location of the i'lash over point at diierent times.

The main object of the invention is, therefore, to provide means for preventing the occurrence of such disruptive discharges at undesirable points such as through the insulation of tbe ma chine and to eiect dissipation of the electrical energy producing such discharges without injury to the insulation or other parts of the apparatus.

This object of the invention is attained by the provision at various points in the circuit of high breakdown-voltage, resistance devices adjusted to have a break-down voltage less than that of the insulating material separating the conduct' ing elements and spaced at intervals so as to insure the presence oi' one of them at or near the point of excessively high potential occurring at different times and in different places. Thus while one of such discharge devices may be inshowing portions of an induction heating ma-v chine with the invention applied thereto.

Fig. 2 is an enlarged fragmentary view showing one form of the high resistance discharge device and its-connection to the apparatus.`

Fig. 3 is an enlarged fragmentary sectional view showing other forms of the discharge device as applied to a pair of concentric conductors and the relation of the conductors to the heating coil and source of current.

Referring to the drawing in detail, the portion of the heat treating apparatus to which the invention is applied comprises an inductive heating coil element I carried by a pair of circuit conductor elements II and I2 which connect the terminals oi' the heating coil to a suitable source of high frequency current which may be the secondary coil I3 of a transformer supplied from a high frequency generator I4. The conductor elements II and I2 are insulated from each other by an intervening sleeve I5 of insulating material. For the sake of compactness such insulation is necessarily relatively thin thus producing an appreciable capacity coupling between the conducting elements but which is suiiciently small, relative to the frequency used, not to interfere with the proper operation of the apparatus.

As shown diagrammatically in Fig. 3 the heating coil I0 is provided with a magnetic core element I6 forming part of a magnetic circuit for the coil, which. magnetic circuit is completed by the work-piece i1 of a permeability which is high relative to that of air. 'I'he apparatus elements thus shown, together with the work-piece I1 forming a part of a low reluctance magnetic circuit for the heating coil I0, constitute an -electrical power transmission -system with an inductive-load Work circuit. The electrical system thus including the work-piece i1 is corrected for optimum power-factor by the condenser IB connected across the circuit near the source I2. Once established such adjustment may remain unchanged so long as the interchangeable work pieces remain substantially identical in certain characteristics such as quality of material, internal structure, shape, size, etc.

Inasmuch as the tendency to disruptive discharge around or through the insulation occurs at diilerent places at different times, the protective disruptive discharge devices are placed at different points along the circuit to insure the presenceof one of them` at or near a high potential zone. For convenience and expediency in installation, such devices are made to vary in form according to the place where they are to be used. However, each of the protective devices .Y consists in general of a high resistance element I9 and an air gap connected in series between the two portions of the apparatus lnear which undue high voltage may occur, and adjusted as to its electrical constants to form a high break-downvoltage resistance device. As indicated in Figures '1 and 2, one such discharge device 2I is shown connected between the lower extremities ,oi' the conductor elements II and I2 near the terminals of the' heating coil III. The discharge device 2I comprises a short cylindrical casing 22 ot insulating material secured to the lower end oi' the inner conductor element II by the metallic screw 22. Within the casing is a leaf lspring elenient 24 bearing at its central portion'against-the head of the screw 22 and at its end portions against contact plate 25 against which bears a resistor YVelement I9 o! 'lh'yrite, the resistance material described "in the patent oi' McEachron No. 1,822,742, dated September 8, 1931, or other suitable resistance material ot characteristics, between which and a second metallic disc 26 is placed a mica disc 21 having an aperture 22 therein providing an air gap 20 between the Thyrite resistor disc I9 and the outer metal disc 26. A metallic cover 29 screwed onto the lower outer portion ofthe casing 22 holds the outer disc 2B against the mica disc 21 through a leaf spring element 20 which also establishes electrical connection between the disc 28 and the metal cover 29. connects the cover 29 with the lower extremity of the outer concentric conductor element I2. Thus the cover element 29 which is electrically connected to the outer conducting element I2 is insulated from the lower extremity of the inner conducting element II by the base of the in sulating box 22 but provides for a disruptive discharge between the lower extremities of the elements I2 and II by way oi' jumper-strip 2i, metallic cover element 29, spring 20, metallic disc 26, air gap 20, Thyrite resistor I9, metallic disc 25, spring 24, and through attaching screw 22 to conductor element II.

For insertion between the concentric conductors the discharge device may take the form shown at 32 in Figures 1 and 3, in which form it consists simply of an annular band 22 ci Thyrite or like resistor material placed around the inner conductor I I and of less wall thickness than the insulating sleeve I5 so as to provide an air gap 34 between the resistor 'element 22 and one of the concentric conductor elements. In the form illustrated the ring of resistance material 33 is iitted in contact with the inner conductor element Il and spaced from the outer conductor t'o form the air gap 22. However, it is to be understood that the resistance element may have -an outside diameter suiicient to place it in contact with the outer conductor I2, and an inside diameter less than the outer diameter of the inner conductor so as to produce an air gap at the outer surface of the inner conductor.

At other places along the circuit formed by conductors II and I2, where desirable or convenient, the discharge device may take the form of that shown at 2l in Figure 3 where it consists simply of a disc or plate 26 oi' resistance material such as Thyrite heid in electrical contact with the inner conductor II by a metallic plug element 21 with an intervening perforated mica disc 28 providing an air gap 29 between the plug 21 and resistance e1ement, the plug 21 being threaded into an opening I. in the outer conducting element I2, establishing electrical contact therewith. VIhus at this point the outer conductor vI2 is maintained insulated from the inner conductor II while a disruptive discharge path is provided between the two conductors by way of the conducting plug 21, air gap 22 and resistance element 22.

The discharge elements may take various other forms according to what form might be most convenient for the particular location chosen,

` to their electrical constants v vide a broken circuit for any the essential feature being that they comprise a resistance element of 'Ihyrite" or similar substance and an air gap connected in series be- Y oi standard voltages such quickly breaks 'down upon A jumper-strip 2| electricallyage rises. The Thyrite thereafter has the characteristic of rapidly lowering its resistance as higher and higher voltages are applied, so that with the high transient voltages, it becomes a virtual short circuit, for as long as the high voltage exists, but immediately becoming restored as soon as that voltage disappears. It will also be understood that the air gap can be omitted, since leakage through the 'Ihyrite" would be almost negligible at ordinary voltages. While a plurality of discharge devices have been shown in various positions, if the point of usual occurrence of discharge of the high voltage appears to be in a single' position, a single device if placed in that position will be found to suflice, For example, a single device 2l such as that shown in Fig. 2, when -properly located, may afford all the protection necessary.

On the other hand by so placing several of the discharge devices at diierent points in the circuit the positioning of one of them at or near a point of high voltage stress is assured.

While I have thus shown and described a specific embodiment of my invention for the sake of disclosure, it is to be understood that the invention is not limited to such specific embodiment but contemplates all such variants and modifications thereot as fall fairly within the scope of the appended claims.

concentric conductors spaced from one another,

a high frequency heat treating coil secured to one end of the arbor and electrically connected lto the conductors, and a protective energy consuming shunt device connected across said concentric conductors at said one end, said device comprising a resistance and an air gap in series, said resistance being of non-linear characteristics such as Thyrite.

2. In a. high power induction heating apparatus, a supporting and conducting arbor having concentric conductors spaced from one another by a sleeve of insulating material, a high frequency heat-treating coil secured to one end of the arbor and electrically connected to the conductors, said sleeve of insulating material being interrupted for a short distance along its length to form an annular gap, and an annular sleeve of resistance material being positioned in said gap and of a thickness less than the insulating material to provide a short air gap between the concentric conductors, said resistance material having non-linear resistance characteristics such as 'I'hyrite.

HOWARD E. SOMES. 

